1. Field of the Invention
The invention relates to an orthodontic component with a base body made from plastic, having a visible face, a base surface spaced at a distance apart therefrom and side faces extending between the latter, at least one slot-shaped recess being arranged in the base body which extends starting from the visible face in a direction towards the base surface and between two oppositely lying side faces, and having an insert element arranged in the recess, as well as a method for its manufacture.
2. The Prior Art
A plastic orthodontic bracket is known from U.S. Pat. No. 5,254,002 A, which is made from a reinforced polycarbonate commonly used for plastic brackets. In order to strengthen it, at least 15% of fibres such as glass fibres, for example, are incorporated in this plastic material. Since the tooth alignment devices from which it is made are subjected to high mechanical stress, for example tensile forces, friction forces, etc. during chewing, and polycarbonate is not capable of withstanding these forces without sustaining damage when used for tooth alignment over a longer period of time, the groove of this tooth alignment device which is usually used to house the tensioning wire is provided with an extra reinforcing element which is stronger than the polycarbonate. The drawback of this is that the higher proportion of fillers used in the polycarbonate on the one hand and the metal reinforcement made of steel on the other have an adverse effect on the translucence and hence the overall appearance of the tooth alignment device. Furthermore, the friction forces transmitted from the tensioning wire to the bracket are not sufficiently reduced to prevent the bracket from suddenly being strained or breaking due to excessive strain, for example during chewing, because the tensioning wire is more easily able to slide off the internal surfaces of the groove in the bracket which receives the tensioning wire.
Another orthodontic component and a method for its manufacture is known from U.S. Pat. No. 5,653,588 A, the orthodontic component being made from a plastic material by an addition polymerisation which is terminated at a temperature corresponding at least to human body temperature. This is of particular importance to the selected plastic because no further changes of state can take place in the material of the bracket during use, particularly in the specific application for which it will be used. In order to strengthen the entire component, at least one reinforcement element can be arranged inside it, improving absorption and damping of the forces which occur during use, in particular pressure caused by chewing and the associated tensile and compression forces, without causing damage to the component. Furthermore, a friction-reducing element is arranged in the slot-shaped recess, which forms the side walls of the slot, at least in certain regions. This friction-reducing element is made from zircon oxide. The selected combination of the plastic and the friction-reducing element could only be used in quite specific applications as tooth attachments for tooth alignment devices.
In other known tooth alignment devices--disclosed in U.S. Pat. No. 1,976,141 A and U.S. Pat. No. 2,045,025 A--the tooth attachments are made from stainless steel and are secured to a stainless steel band which encircles the tooth in order to hold the tooth attachment in the appropriate position.
Various other tooth alignment methods and tooth alignment devices have been developed in which stainless steel tooth attachments are cemented directly onto the surface of the tooth. These methods and devices require no band to secure the tooth attachments. Such systems are often used. Tooth alignment methods and devices of this type are known amongst others from U.S. Pat. Nos. 4,604,057 A, 4,430,061 A and 4,322,206 A. The drawback of such stainless steel tooth attachments is their metallic appearance. Therefore, for reasons of appearance, adult patients in particular desire orthodontic devices which are not made of metal but of transparent or translucent materials, as such materials provide improved cosmetic appearance. Accordingly, transparent plastic materials are used, mostly polycarbonates or transparent or translucent ceramic materials made from aluminium oxide. In known tooth attachments consisting of non-metallic materials and produced in very small sizes to keep cosmetic drawbacks at a minimum, a known approach--disclosed in U.S. Pat. No. 4,302,532 A--is to increase the strength of ceramic tooth attachments made from plastic by using reinforcing elements.
Tooth alignment devices with a ceramic tooth attachment made from a polycrystalline ceramic structure with various additives are also known. One known ceramic tooth attachment--disclosed in U.S. Pat. No. 4,954,080 A--consists of polycrystalline ceramic having a light transmission in the visible spectrum, which reduces the visibility of this tooth attachment so that when it is mounted on the tooth, it can be hardly recognised by a third party. This polycrystalline ceramic body for the ceramic tooth attachment is produced by pressing powdered high purity aluminium oxide, which is then sintered to present a close to zero porosity and an average grain size in the range of 10 to 30 micrometers. Preferably, the tooth attachment should be colourless. An in-line light transmission in the visible spectrum should be 20% to 60% through a specimen having a thickness of 0.5 mm.